Added unittest for writing directories.

[travcunn]

No description provided.

[travcunn]

Since the Travis CI build is not setup correctly, here are the test results:

▶ py.test tests.py -v 
=========================== test session starts ===========================
platform linux2 -- Python 2.7.8 -- py-1.4.27 -- pytest-2.7.0 -- /home/travis/venv/bin/python2
rootdir: /home/travis/python-libarchive, inifile: 
collected 15 items 

tests.py::TestIsArchiveName::test_formats PASSED
tests.py::TestIsArchiveZip::test_zip PASSED
tests.py::TestIsArchiveTar::test_tar PASSED
tests.py::TestZipRead::test_close_stream_first PASSED
tests.py::TestZipRead::test_deferred_close_by_archive PASSED
tests.py::TestZipRead::test_deferred_close_by_stream PASSED
tests.py::TestZipRead::test_extract_str PASSED
tests.py::TestZipRead::test_filenames PASSED
tests.py::TestZipRead::test_iszipfile PASSED
tests.py::TestZipRead::test_iterate PASSED
tests.py::TestZipWrite::test_deferred_close_by_archive PASSED
tests.py::TestZipWrite::test_writepath PASSED
tests.py::TestZipWrite::test_writepath_directory PASSED
tests.py::TestZipWrite::test_writestream PASSED
tests.py::TestZipWrite::test_writestream_unbuffered PASSED

======================== 15 passed in 0.04 seconds ========================